[Lucio]

Could be fairly simple.

The CCTV system could have an auto adjust feature on the brightness, to try and pick out more detail if the motion is detected in a "dark" area.

So there's a small rodent or something moving in an already dark frame, CCTV goes "hang on, movement there, better enchance the light level". With the bulb already being really quite bright it'll just overwhelm the sensor, because the dark area will seem to be not getting bright enough no matter what the camera is doing.